The Arabidopsis calcium sensor calcineurin B-like 3 inhibits the 5'-methylthioadenosine nucleosidase in a calcium-dependent manner.
Calcineurin B-like (CBL) proteins represent a unique family of calcium sensors in plant cells. Sensing the calcium signals elicited by a variety of abiotic stresses, CBLs transmit the information to a group of serine/threonine protein kinases (CBL-interacting protein kinases [CIPKs]), which are currently known as the sole targets of the CBL family. Here, we report that the CBL3 member of this family has a novel interaction partner in addition to the CIPK proteins. Extensive yeast two-hybrid screenings with CBL3 as bait identified an interesting Arabidopsis (Arabidopsis thaliana) cDNA clone (named AtMTAN, for 5'-methylthioadenosine nucleosidase), which encodes a polypeptide similar to EcMTAN from Escherichia coli. Deletion analyses showed that CBL3 utilizes the different structural modules to interact with its distinct target proteins, CIPKs and AtMTAN. In vitro and in vivo analyses verified that CBL3 and AtMTAN physically associate only in the presence of Ca(2+). In addition, we empirically demonstrated that the AtMTAN protein indeed possesses the MTAN activity, which can be inhibited specifically by Ca(2+)-bound CBL3. Overall, these findings suggest that the CBL family members can relay the calcium signals in more diverse ways than previously thought. We also discuss a possible mechanism by which the CBL3-mediated calcium signaling regulates the biosynthesis of ethylene and polyamines, which are involved in plant growth and development as well as various stress responses.
Oh
Seung-Ick
SI
Department of Molecular Biology, Sejong University, Seoul 143-747, Korea.
Park
Jimyeong
J
Yoon
Sunhee
S
Kim
Yungyeong
Y
Park
Soojin
S
Ryu
Migyeong
M
Nam
Min Jung
MJ
Ok
Sung Han
SH
Kim
Jeong-Kook
JK
Shin
Jeong-Sheop
JS
Kim
Kyung-Nam
KN
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology*; D020013:Calcium Signaling / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D005966:Glucuronidase / Q000032:analysis; D049452:Green Fluorescent Proteins / Q000032:analysis; D008969:Molecular Sequence Data; D019697:Onions / Q000235:genetics; D025941:Protein Interaction Mapping; D011683:Purine-Nucleoside Phosphorylase / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000032:analysis; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
D029681:Arabidopsis Proteins; C484079:CBL3 protein, Arabidopsis; D002135:Calcium-Binding Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; D005966:Glucuronidase; D002118:Calcium